This invention is related generally to the field of Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), Near field Scanning Optical Microscopy (NSOM), NanoSpectroPhotometry (NSP), NanoPolarimetry (NP), Magnetic Field Microscopy (MFM) and any other methods adaptable and suitable to guide the scanning and nanomachining techniques described herein. These technologies are sometimes collectively referred to as Scanning probe Microscopy (SPM). Generally, SPM technologies allow one to “see” atomic-scale features on or in surfaces.
An AFM works by scanning a tip over a surface much the same way as a phonograph needle scans a record. The tip is located at the end of a cantilever beam and positioned over the surface to be scanned. The combination of the cantilever beam and tip is sometimes referred to collectively as a scanning probe or simply a probe.
AFM techniques rely on the effects of the inter-atomic interactions, such as van der Waals forces, that arise between the atoms in the structure of the tip and the atoms at the surface being imaged. As the tip is attracted to the surface, the cantilever beam is deflected. The magnitudes of the deflections correspond to the topological features of the atomic structure of the surface being scanned. The AFM can work with the tip touching the sample (contact mode), or the tip can tap across the surface (tapping mode), or made to not touch the surface at all (non-contact mode, which is the preferred embodiment).
STM techniques rely on the fact that the electron probability cloud associated with the atoms at the surface extends a very small distance above the surface as described by the quantum physical model. When a tip is brought sufficiently close to such a surface, there is an increasingly stronger probability of an interaction (current) between the electron cloud on the surface and that of the tip atom. An electric tunneling current flows when a small voltage is applied. The tunneling current is very sensitive to the distance between the tip and the surface. These changes in the tunneling current with distance as the tip is scanned over the surface are used to produce an image of the surface.
Nanomachining involves removal, addition, or movement of material on a surface in a controlled manner to attain specific surface features. Typically, an appropriate scanning probe is manipulated so that its tip comes into contact with a surface to be nanomachined. The scanning probe is then translated along a pre-programmed vector, producing a scraping action across the contacted surface and removing an amount of material from the surface. An appropriate feed is applied to control the amount of material removed. This is repeated until the desired features are achieved. Any surface which is exposed to contact by the scanning probe can be nanomachined. Thus, for example the walls of a vertical structure can be nanomachined using a scanning probe having an appropriately shaped tip applied to the wall with an appropriate feed force.
FIG. 1 is a generalized diagram illustrating a typical SPM system 10. A scanning probe 12 is the workhorse of the SPM. A typical probe comprises a cantilever and a tip disposed at the free end of the cantilever. Various tip shapes and configurations suitable for scanning and nanomachining are disclosed in the various above-identified commonly owned issued patents and commonly owned, co-pending patent applications.
FIG. 2 shows a typical arrangement of a scanning probe 12 suitable for use with the present invention. A cantilever 14 is attached to a body member 16 which provides structure for attachment to a probe translation apparatus. Disposed at the free end of the cantilever is an appropriately shaped probe tip 102. The particular dimensions of the probe will vary depending on the particular application.
Referring back to FIG. 1, the probe 12 can be coupled to a first translation stage 18. The first translation stage can provide movement of the probe in the X-Y plane. By convention, the X-Y plane is the plane parallel to the major surface of a workpiece 20. Thus, the probe can be positioned in the X-Y position relative to the workpiece by the first translation stage. The first translation stage can also provide movement of the probe in the Z-direction and thus position the probe in three-dimensional space relative to the workpiece. Such first translation stages are known and well understood devices. Typically, they are piezoelectric devices.
Alternatively or in addition, a second translation stage 22 can be provided. The workpiece 20 can be affixed to the second translation stage to provide X-Y motion of the workpiece relative to the probe 12. Furthermore, the second translation stage can provide motion of the workpiece in the Z direction relative to the probe. Such stages are typically linear motors, or precision ball screw stages or combinations thereof with linear scale or interferometric position feedback.
The relative motion between the probe 12 and the workpiece 20 can be achieved by any of a number of techniques. The probe can be translated in three dimensions while maintaining the workpiece in a stationary position. Conversely, the workpiece can move relative to a stationary probe. Both the probe and the workpiece can be moved in a coordinated fashion to achieve rapid positioning. The first translation stage 104 might provide only X-Y motion, while Z-axis positioning is provided by the second translation stage 106; or vice-versa. These and still other combinations of concerted motions of the probe and the workpiece can be performed to effect relative motion between the probe and the workpiece.
A detection module 24 is coupled to detect signal received from the scan probe 12. Many detection techniques are known. For example, if the probe is operated in AFM (atomic force microscopy) mode, the cantilever resonance point is shifted by the interatomic forces acting between the tip and the surface as the tip is scanned across the surface. A generalized controller 26 can be configured to provide various computer-based functions such as controlling the components of the system 10, performing data collection and subsequent analysis, and so on. Typically, the controller is some computer-based device; for example, common architectures are based on a microcontroller, or a general purpose CPU, or even a custom ASIC-based controller. A user interface 28 is provided to allow a user to interact with the system. The “user” can be a machine user. A machine interface might be appropriate in an automated environment where control decisions are provided by a machine.
A data store 30 contains various information to facilitate scanning and nanomachining operations and for overall operation of the system 10. The data store contains the programming code that executes on the controller 26. The data store shown in the figure can be any appropriate data storage technology, ranging from a single disk drive unit to a distributed data storage system.
Typically, traditional Scanning Probe Microscopy (SPM) and other measurement systems employ a conventional raster scanning technique to collect measurements within a region of interest. Such a conventional raster scanning technique involves taking measurements in rows, referred to as a raster pattern. That is, the region of interest is mapped by a plurality of parallel, equally-spaced scan lines. The tip of a measurement probe begins at the first sample point on the first scan line and moves along the first scan line, collecting data at each sample point, until it finishes collecting data on the last sample point of the first scan line. Then, the tip moves to the first sample point on the second scan line and begins collecting data along the second scan line in a similar fashion. The process thus repeats for the remaining scan lines until the tip completes the last measurement at the last sample point, at the end of the last scan line.
Taking measurements using a conventional raster scanning technique can be extremely time-consuming and inefficient. Such measurements on a region of interest are completed only after the last measurement on the last scan line is made. Scanning in such a fashion can waste time and resources by collecting data at unimportant sample points or inefficiently spaced sample points. For example, measurements may only need to be taken on a particular structure located within the region of interest. However, the exact location of the structure may not be known. There may only be probabilistic information regarding the location of the structure. Furthermore, measurement may only need to be taken on particular regions of the structure. Also, it may be the case that only measurements that fall within certain value ranges are of interest.
With conventional raster scanning techniques, many of these problems cannot be solved by simply adjusting the number of sample points in a scan line or the spacing between scan lines. In a wide range of applications, useful data must be collected with greater speed and efficiency, in a manner that takes into account the type of measurement needed.